An example of a prior-art apparatus is, for example, an apparatus which is disclosed in Patent Document 1 indicated below.
The apparatus stated in Patent Document 1 includes fuses in the respective phases of an inverter, and in an abnormal state where any switching element short-circuits, the apparatus prevents a brake torque ascribable to induced power in such a way that a current which is larger than in an abnormal state is caused to flow through a short-circuiting path, thereby to blow out the fuse and to open a closed circuit passing through the short-circuiting place.
Besides, an example of another prior-art apparatus is an apparatus which is disclosed in Patent Document 2 indicated below.
The apparatus stated in Patent Document 2 is such that, in an abnormal state where two phases short-circuit therebetween among the wires of three phases as connect a three-phase electric motor and switching elements, motor relays disposed in the wires are held closed without being opened, thereby to continue controllable states. Besides, any overcurrent is suppressed by limiting duties so that the upper switching elements and lower switching elements of the two phases having short-circuited may not fall into their ON states at the same time.    Patent Document 1: JP-A-2003-81099    Patent Document 2: JP-A-2005-153570